The present invention relates generally to optics, and more particularly, to ultra-wide band signal generation using digitally jointed dual sidebands and RF up-conversion for single optical carrier transmission.
The following references are noted herein in the background discussion of the application:                [1] Y.-K. Huang, et. al., “10×456-Gb/s DP-16QAM transmission over 8×100 km of ULAF using coherent detection with a 30-GHz analog-to-digital converter,” OECC 2010, PDP3, Sapporo, July 2010.        [2] F. Buchali, et. al., “1-Tbit/s dual-carrier DP 64QAM transmission at 64Gbaud with 40% overhead soft-FEC over 320 km SSMF,” OFC/NFOEC 2013, OTh4E.3, Los Angeles, Calif., March 2013.        [3] G. Raybon, et. al., “Single-carrier 400G interface and 10-channel WDMtransmission over 4,800 km using all-ETDM107-Gbaud PDM-QPSK,” OFC/NFOEC 2013, PDP5A.5, Los Angeles, Calif., March 2013.        [4] G. Raybon, et. al., “All-ETDM107-Gbaud PDM-16QAM (856-Gb/s) Transmitter and Coherent Receiver,” ECOC 2013, PD2.D.3, London, September 2013.        
Riding on the success of commercial 100 GbE deployments, the quest for technologies that can scale transmission capacity to 400-Gb/s or 1-Tb/s has become a key theme in optical communication research. Most of the experimental demonstrations presented thus far have focused on multi-carrier transmission, such as 4×100G dual-polarization (DP) quadrature phase shifted keying (QPSK), or dual-carrier 2×200G DP-16-quadrature amplitude-modulated (QAM) transmission for 400G-Gb/s. For networks with shorter reach requirements, technologies with higher spectral efficiency such as dual-carrier DP-16QAM is preferable because of the potential to lower the cost per transmitted bit since fewer subcarriers undergo parallel modulation/detection operations. In metro networks, where the number of connections is quite high, it is even more critical to reduce the cost per transponder. Therefore many system vendors are considering the option of switching from dual-carrier to single-carrier transponders, so that it is possible to further reduce cost since the number of RF and optical components, including drivers, modulators, and photodiodes can be halved.
Several recent publications have shown single carrier operation with beyond 400-Gb/s transmission capacity. In [1], optical time division multiplexing (OTDM) was used, such that parallel modulation was still required. A DP-64QAM single carrier signal was shown to support 500-Gb/s transmission in [2], but its low OSNR tolerance and higher DSP complexity may incur practical implementation delays. In [3,4], ultra-high symbol rate transmission was achieved for both DP-QPSK and DP-16QAM by first generating binary electrical signals using high-speed electrical data multiplexer. There are two drawbacks with this scheme. First, since the signal is generated using electrical multiplexers and could be classified as an “analog transmitter,” it would be difficult to perform spectral shaping on the baseband electrical waveforms, an important function which the new generation of “digital transmitters” equipped with DAC is capable of doing. Secondly, DSP chips available now for coherent transmission system have a maximum operating rate ˜32 Gbaud. To support ultra-high baud-rate operations, it would require huge investment from the chip designers to at least double the operation bandwidth of the DAC and ADC on chip, with possible compromise in power consumption, while the major applications that would most likely adopt single carrier technology are those that require lower cost and energy efficiency, such as metro and datacenter networks.
Accordingly, there is a need for a solution to for ultra wide band signal generation that overcomes limitations of prior efforts.